Surface roughness dominated wettability of carbon fiber in gas diffusion layer materials revealed by molecular dynamics simulations

High water contact angle in carbon fiber can facilitate water removal ability of gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs). Water contact angle is intensively dependent on the surface hydrophobicity of carbon fiber in GDL. In this study, the hydrophobicity of commercial GDL is enhanced through the immersion and hydrothermal methods. The porosity decreases slightly while the surface roughness and surface topology diversity increase significantly in hydrothermal GDL compared with commercial reference and immersion GDL samples. The molecular dynamics simulations show that the water contact angle increases significantly with the increasing surface roughness but varies slightly with different surface topology, indicating that the water contact angle is dominated by the surface roughness. This study's findings are expected to offer an approach that can effectively enhance the water removal capacity by tailoring the surface roughness of carbon fibers in GDL materials.